[POWERPC] cell: abstract spu management routines

This adds a platform specific spu management abstraction and the coresponding
routines to support the IBM Cell Blade.  It also removes the hypervisor only
resources that were included in struct spu.

Three new platform specific routines are introduced, spu_enumerate_spus(),
spu_create_spu() and spu_destroy_spu().  The underlying design uses a new
type, struct spu_management_ops, to hold function pointers that the platform
setup code is expected to initialize to instances appropriate to that platform.

For the IBM Cell Blade support, I put the hypervisor only resources that were
in struct spu into a platform specific data structure struct spu_pdata.

Signed-off-by: Geoff Levand <geoffrey.levand@am.sony.com>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>